TEHRAN, Iran -- Iran will "take a strong step" away from its 2015 nuclear deal with world powers if Europe cannot offer the country new terms by a deadline at the end of this week, a government spokesman said Monday as top Iranian diplomats travelled to France and Russia for last-minute talks.

The comments from Ali Rabiei reinforced the Friday deadline Iran had set for Europe to offer it a way to sell its crude oil on the global market.

Crushing U.S. sanctions imposed after U.S. President Donald Trump withdrew the U.S. from the deal have curbed Iran's oil exports and sent its economy into freefall.

In response, Iran has surpassed limits on nuclear enrichment set out in the accord in a bid to pressure Europe to find a way around the U.S. sanctions.

Iranian Foreign Minister Mohammad Javad Zarif was in Moscow, while his deputy travelled to Paris with a team of economists Monday in a renewed diplomatic push.

The developments come after French President Emmanuel Macron surprised the Group of Seven summit in France by inviting Zarif last week.

Rabiei described Iran's strategy to journalists at Monday's press conference in Tehran as "commitment for commitment."

"Iran's oil should be bought and its money should be accessible to return to Iran," Rabiei said. "This is the agenda of our talks."

It's unclear what the terms of negotiation are. In theory, anyone caught buying Iranian crude oil would be subject to U.S. sanctions and potentially locked out of the American financial market.

An Iranian lawmaker on Sunday said France has proposed a $15 billion credit line in three phases to pre-purchase Iranian oil, the semi-official Tasnim news agency reported.

In exchange, Iran would halt steps it's taken to break away from the deal and return to full compliance, lawmaker Ali Motahari was quoted as saying.

Negotiations continued as just last week the International Atomic Energy Agency confirmed that Iran's stockpile of low-enriched uranium still exceeds the amount allowed by the so-called Joint Comprehensive Plan of Action, or JCPOA as the deal is known.

The UN agency also said Iran continues to enrich uranium up to 4.5%, above the 3.67% allowed.

Enriched uranium at the 3.67% level is enough for peaceful pursuits and is far below weapons-grade levels of 90%. At the 4.5% level, the uranium can help power Iran's Bushehr reactor, the country's only nuclear power plant.

It remains unclear what further step Iran could take, though it could involve restarting advanced centrifuges prohibited by the deal or further bumping up its enrichment of uranium. Iran insists the steps it has taken so far are easily reversible.

"We will announce implementation of the third step in a letter to the Europeans if the Europeans do not implement necessary measures by Thursday," said Zarif in a Sunday interview with Iran's parliament news agency, ICANA.

Meeting in Moscow with his Russian counterpart Sergey Lavrov, Zarif reiterated that it was up to Europe to ensure the deal's survival.

Iran will "be complying with its obligations in full when the Europeans comply with theirs in full," Zarif told journalists.

The nuclear deal is meant to keep Tehran from building atomic weapons in exchange for economic relief. It has been complicated by the unilateral withdrawal of the United States from the deal and Washington's increased sanctions on Tehran, which have been taking a toll on the Iranian economy.

That has left the other signatories -- Germany, Britain, France, Russia and China -- struggling to come up with enough incentives to keep Iran in the deal.

"Iran is willing to give Diplomacy, Engagement and Dialogue another chance," Iranian Foreign Ministry spokesman Abbas Mousavi wrote on Twitter, but added that "Opportunities pass like clouds."

Meanwhile Monday, an Iranian oil tanker pursued by the U.S. that has been travelling across the Mediterranean Sea is now off the coast of Tripoli in northern Lebanon. The ship-tracking website MarineTraffic.com showed the Adrian Darya 1 moving slowly just outside the Lebanese territorial waters, after it had stood off the coast of Syria a day earlier.

U.S. Secretary of State Mike Pompeo has alleged the ship is bound for a refinery in Syria, which was the reason that authorities had seized the vessel off the coast of Gibraltar in July. The U.S. has warned countries not to accept the Adrian Darya, which carries 2.1 million barrels of Iranian crude oil worth some US$130 million.

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Associated Press writers Zeina Karam in Beirut, Nataliya Vasilyeva in Moscow and Jon Gambrell in Dubai, United Arab Emirates, contributed to this report.